The present invention is directed toward photoconductors and compositions used to form photoconductors. More particularly, the invention is directed toward photoconductors comprising a substrate and a layer selected from the group consisting of charge transfer layers comprising a charge transfer molecule, polycarbonate and a first polyaryl ether; charge generating layers comprising a pigment, polyvinylbutyral and a second polyaryl ether; and mixtures thereof. The invention is also directed toward methods of improving the electrical characteristics of photoconductors, methods of extending the pot-life of charge transport compositions, and compositions used to form charge transport layers and charge generation layers.
In electrophotography, a latent image is created on the surface of an imaging member such as a photoconducting material by first uniformly charging the surface and then selectively exposing areas of the surface to light. A difference in electrostatic charge density is created between those areas on the surface which are exposed to light and those areas on the surface which are not exposed to light. The latent electrostatic image is developed into a visible image by electrostatic toners. The toners are selectively attracted to either the exposed or unexposed portions of the photoconductor surface, depending on the relative electrostatic charges on the photoconductor surface, the development electrode and the toner.
Typically, a dual layer electrophotographic photoconductor comprises a substrate such as a metal ground plane member on which a charge generation layer (CGL) and a charge transport layer (CTL) are coated. The charge transport layer contains a charge transport material which comprises a hole transport material or an electron transport material. For simplicity, the following discussions herein are directed to use of a charge transport layer which comprises a hole transport material as the charge transport compound. One skilled in the art will appreciate that if the charge transport layer contains an electron transport material rather than a hole transport material, the charge placed on a photoconductor surface will be opposite that described herein.
When the charge transport layer containing a hole transport material is formed on the charge generation layer, a negative charge is typically placed on the photoconductor surface. Conversely, when the charge generation layer is formed on the charge transport layer, a positive charge is typically placed on the photoconductor surface. Conventionally, the charge generation layer comprises the charge generation compound or molecule, for example a squaraine pigment, a phthalocyanine, or an azo compound, alone or in combination with a binder. The charge transport layer typically comprises a polymeric binder containing the charge transport compound or molecule. The charge generation compounds within the charge generation layer are sensitive to image-forming radiation and photogenerate electron-hole pairs therein as a result of absorbing such radiation. The charge transport layer is usually non-absorbent of the image-forming radiation and the charge transport compounds serve to transport holes to the surface of a negatively charged photoconductor. Photoconductors of this type are disclosed in the Adley et al U.S. Pat. No. 5,130,215 and the Balthis et al U.S. Pat. No. 5,545,499.
Allen et al., U.S. Pat. No. 5,322,755, teach a layered polyconductive imaging member comprising a substrate, a photogenerator layer and a charge transport layer. Allen et al. teach the photogenerator layer comprises a binder mixture of two or more polymers such as polyvinylcarbazole, polycarbonates, polyvinylbutyral and polyesters.
Nogami et al., U.S. Pat. No. 5,725,982, teach photoconductors comprising a charge transport layer comprising an aromatic polycarbonate resin. Nogami et al. further teach the photoconductor may comprise a charge generating layer comprising resins such as polycarbonate resin, polyvinylbutyral, polyacrylic ester, polymethacrylic ester, vinylchloride based copolymer, polyvinylacetal, polyvinylpropional, phenoxy resin, epoxy resin, urethane resin, cellulose ester and cellulose ether.
Nakamura et al., U.S. Pat. No. 5,837,410, teach a photoconductor comprising a conductive layer and an organic film. Nakamura et al. teach that the organic film may comprise a charge-generating layer which comprises binders such as polyvinylbutyral resin, polyvinylchloride copolymer resin, acrylic resin, polyester resin and polycarbonate resin and a charge transport layer comprising resins such as polyester resin, polycarbonate resin, polymethacrylic resin and polystyrene resin.
Polyarylether ketones can be synthesized in art recognized ways, such as the method taught by Kelsey, U.S. Pat. No. 4,882,397, Rose, U.S. Pat. No. 4,419,486, and Roovers et al., U.S. Pat. No. 5,288,834. Kelsey teaches a process for preparing polyarylether ketones from a polyketal. Rose teaches sulfonation of polyarylether ketones. Roovers et al. teach bromomethyl derivatives of polyarylether ketones are useful intermediates for further functionalizing the aromatic polyether ketones, and further teach functionalized polyarylether ketones such as carbonyl fluoride poly (aryl ether ether ketone), cyan methylene poly(aryl ether ether ketone), diethylamine methylene poly(aryl ether ether ketone), and aldehyde polyaryl (aryl ether ether ketone).
Nakamura et al., EP 0501455 A1, teach a photoconductor comprising a substrate and a photosensitive layer comprising a charge generating layer and a charge transporting layer. Nakamura et al. teach the charge generating layer contains an organic pigment and a polyarylether ketone binder resin.
Japanese Patent Application JP 63239454 A teaches an electrophotographic sensitive body comprising a layer containing a polyetherketone binder resin, while Japanese Patent Application JP 632247754 A teaches an electrophotographic sensitive body comprising a charge transfer layer comprising a hydrazone compound charge transfer material and a polyetherketone resin. Japanese Application JP 63070256 A teaches a photoconductive layer comprising a polyetherketone resin laminated on a conductive base.
Kan et al., U.S. Pat. No. 4,772,526, disclose a reusable electrophotographic imaging element having a photoconductive surface layer in which the binder resin comprises a block copolyester or copolycarbonate having a fluorinated polyether block. Kan et al. teach that the surface layer is either capable of generating an injecting charge carriers upon exposure, or capable of accepting and transporting injected charge carriers.
Mxc3xcller, U.S. Pat. No. 5,006,443, discloses perfluoralkyl group-containing polymers which are useful in radiation-sensitive reproduction layers. Mxc3xcller teaches the perfluoroalkyl group-containing polymers comprise polymers or polycondensates and have phenolic hydroxyl groups and perfluoroalkyl groups which are optionally attached through intermediate members.
Ishikawa et al., U.S. Pat. No. 5,073,466, disclose an electrophotographic member comprising a support, a photoconductive layer, and a surface layer comprising a lubricating agent and a fixing group. Ishikawa et al. teach the lubricating agent has a perfluoropolyoxyalkyl group or a perfluoropolyoxyalkylene group.
Suzuki, et al., U.S. Pat. No. 5,344,733, disclose an electrophotographic receptor having an overcoat layer on the surface of a photosensitive layer containing a charge generating substance. Suzuki et al. teach the overcoat layer comprises a fluororesin cured with a melamine compound or an isocyanate compound as a cross-linking agent, a charge generating substance, and a charge transport substance.
The charge transport layer and charge generation layers of photoconductors generally comprise binders. For example, the charge generation layer generally comprises pigments, however, since pigments do not adhere effectively to metal substrates, polymer binders are usually included. Unfortunately, the electrical sensitivity of the charge generation layer, drum wear, or composition pot-life can be affected by the polymer binder.
For example, the use of polyvinylbutyral as a charge generation layer binder is advantageous in that it significantly improves adhesion of the charge generation layer to the substrate. Unfortunately, polyvinylbutyral can disadvantageously affect electrical characteristics of the resulting photoconductor in causing, inter alia, high dark decay and residual voltage properties.
Polycarbonates have been known to improve the mechanical properties of a photoconductor, particularly its impact resistance. Unfortunately, the use of polycarbonates can result in photoconductors which are susceptible to drum-end wear, which may result in print-quality defects or drum failure, and to scratches in the paper area, which may lead to print-quality defects.
The use of polytetrafluoroethylene results in photoconductor drums exhibiting lower coefficients of friction and higher abrasion resistance. Unfortunately, polytetrafluoroethylene tends to settle in the transport composition, therefore adversely affecting the pot-life of the composition.
Accordingly, it is an object of this invention to obviate various problems of the prior art.
It is another object of this invention to provide photoconductors having good electrical characteristics, particularly electrical sensitivity, and reduced dark decay.
It is a further object of this invention to provide photoconductors which have improved print-stability and fatigue characteristics.
It is another object of this invention to provide charge transport compositions having extended pot-life.
It is an object of this invention to provide photoconductors exhibiting low electrical fatigue and stable print-performance.
In accordance with one aspect of the invention there are provided photoconductors comprising a substrate and at least one layer selected from the group consisting of:
a) charge transfer layers comprising a charge transfer molecule, polycarbonate and a first polyaryl ether selected from the group consisting of polyaryletherketones, poly(aryl-perfluoroaryl ether)s, polyaryletherketone-hydrazones, polyaryletherketone-azines and mixtures and copolymers thereof;
b) charge generation layers comprising a pigment, polyvinylbutyral and a second polyaryl ether selected from the group consisting of polyaryletherketones, polyarylethersulfones and mixtures and copolymers thereof; and
c) mixtures thereof.
In accordance with another aspect of the invention there is provided methods of improving one or more electrical characteristics of photoconductors. The methods comprise the step of forming photoconductors comprising a substrate and at least one layer selected from the group consisting of:
a) charge transfer layers comprising a charge transfer molecule, polycarbonate and a first polyaryl ether selected from the group consisting of polyaryletherketones, poly(aryl-perfluoroaryl ether)s, polyaryletherketone-hydrazones, polyaryletherketone-azines and mixtures thereof;
b) charge generating layers comprising a pigment, a polyvinylbutyral and a second polyaryl ether selected from the group consisting of polyaryletherketones, polyarylethersulfones and mixtures thereof; and
c) mixtures thereof.
When the photoconductor comprises a charge transfer layer comprising a polyarylether ketone, the weight ratio of polycarbonate to polyarylether ketone is preferably from about 93:7 to about 86:14.
In accordance with another aspect of the invention there are provided methods of extending the pot-life of a charge transport composition. The methods comprise the step of providing polyaryl ethers selected from the group consisting of polyaryletherketones, poly(aryl-perfluoroaryl ether)s, polyaryletherketone-hydrazones, polyaryletherketone-azines and mixtures thereof in combination with polycarbonate and a charge transport molecule.
In accordance with a further aspect of the invention there are provided charge transfer compositions comprising a charge transfer molecule, solvent and a binder blend. The binder blend comprises polycarbonate and a polyaryl ether selected from the group consisting of polyaryletherketones, poly(aryl-perfluoroaryl ether)s, polyaryletherketone-hydrazones, polyaryletherketone-azines and mixtures thereof.
In accordance with yet another aspect of the invention there are provided charge generation compositions comprising pigment, solvent and a binder blend. The binder blend comprises polyvinylbutyral and a polyaryl ether selected from the group consisting of polyaryletherketones, polyarylethersulfones and mixtures thereof.
In accordance with yet another aspect of the invention there are provided methods of preparing modified polyaryletherketones comprising the step of condensing polyaryletherketones with a reagent selected from the group consisting of hydrazines and hydrazones.
It has been found that photoconductors in accordance with the present invention have good electrical characteristics, low electrical fatigue and stable print-performance. Further, it has been found that charge transport compositions in accordance with the present invention have improved extended pot-life.
These and additional objects and advantages will be more fully apparent in view of the following description.
The charge transport and charge generation layers according to the present invention are suitable for use in dual layer photoconductors. Such photoconductors generally comprise a substrate, a charge generation layer (CGL) and a charge transport layer (CTL). The photoconductors may also comprise a sub-layer to assist in the adhesion of the charge generation and charge transport layers, or a protective coating to reinforce the durability of the charge generation and charge transport layers. Some substrates, such as aluminum, may be anodized.
While various embodiments of the invention discussed herein refer to the charge generation layer as being formed on the substrate, with the charge transport layer formed on the charge generation layer, it is equally within the scope of the present invention for the charge transport layer to be formed on the substrate with the charge generation layer formed on the charge transport layer.
The present invention is directed toward photoconductors, and more particularly to photoconductors comprising charge transport layers and/or charge generation layers comprising binder blends containing a polyaryl ether. Photoconductors comprising charge generation layers and/or charge transfer layers in accordance with the present invention exhibit improved electrical characteristics such as improved photosensitivity, reduced dark decay, and reduced fatigue.
As used herein, xe2x80x9ccardo groupsxe2x80x9d refers to cyclic groups that tend to form a loop in the polymer chain. Cardo groups include cyclohexyl, fluorenyl and phthalidenyl groups.
As used herein, xe2x80x9ccharge voltagexe2x80x9d refers to the voltage applied on a drum by a charge roll or corona. xe2x80x9cDischarge voltagexe2x80x9d refers to the voltage on the drum after shining light on the drum. Discharge voltage may be measured at several different light energies. Whereas the streak voltage corresponds to the voltage measured at the lower laser light energy (about 0.2 microjoules/cm2), the discharge voltage (also referred to as residual voltage) corresponds to voltage at the higher laser energy.
Photoconductor drums may exhibit a loss of charge in the dark, i.e., may lose some charge before a light source discharges the charge. As used herein, xe2x80x9cdark decayxe2x80x9d refers to the loss of charge from the surface of a photoconductor when it is maintained in the dark. Dark decay is an undesirable feature as it reduces the contrast potential between image and background areas, leading to washed out images and loss of gray scale. Dark decay also reduces the field that the photoconductive process will experience when light is brought back to the surface, thereby reducing the operational efficiency of the photoconductor.
As used herein, xe2x80x9cfatiguexe2x80x9d refers to the tendency for a photoconductor to exhibit increases(negative) or decreases (positive) in its discharge voltage. Fatigue is undesirable as it reduces the development factor resulting in light or washed out print or dark print, as well as print that varies from page to page.
As used here, xe2x80x9csensitivityxe2x80x9d or xe2x80x9cphotosensitivityxe2x80x9d refers to the ability of a photoconductor to discharge its voltage efficiently. The photosensitivity may be measured as the amount of light energy, in microjoules/cm2, required to reduce the photoconductor""s voltage from its initial charge to a lower charge. The photoconductors may be subjected to sensitivity measurements using a sensitometer fitted with electrostatic probes to measure the voltage magnitude as a function of light energy shining on the photoconductor surface. It is undesirable for a photoconductor to have poor sensitivity for such a photoconductor would require a large amount of light energy to discharge its voltage.
Additionally, the present invention is directed toward compositions used to form CTLs and CGLs, referred to as xe2x80x9ccharge transport compositionsxe2x80x9d and xe2x80x9ccharge generation compositionsxe2x80x9d. Charge transport compositions in accordance with the present invention show improved pot-life. As used here, xe2x80x9cpot-lifexe2x80x9d refers to the length of time a composition, particularly a charge transport composition used to prepare a charge transport layer, can be stored without the composition becoming too viscous to be easily applied to a substrate and without the resulting layer exhibiting any adverse effects. Preferably the earliest layer formed by the composition and the latest layer formed by the composition have substantially similar characteristics. If the characteristics of the earlier layers differ from the later layers, it may be necessary to dispose of and replace the composition even though it has not yet become so viscous that it is difficult to apply. It is advantageous for a composition to have a long pot-life in order to avoid frequent disposal and replacement of the composition.
Photoconductors of the present invention comprise a substrate and at least one layer selected from the group consisting of:
a) charge transfer layers comprising a charge transfer molecule, polycarbonate and a first polyaryl ether selected from the group consisting of polyaryletherketones, poly(aryl-perfluoroaryl ether)s, polyaryletherketone-hydrazones, polyaryletherketone-azines, and mixtures thereof;
b) charge generating layers comprising a pigment, polyvinylbutyral and a second polyaryl ether selected from the group consisting of polyaryletherketones, polyarylethersulfones and mixtures thereof; and
c) mixtures thereof.
Polyaryl Ethers
As used herein, xe2x80x9cpolyaryl ethersxe2x80x9d is intended to refer to polymers having a backbone comprising aromatic groups and ether linkages. The polyaryl ether polymers include both homopolymers and copolymers. The copolymers comprise at least two different monomer units, wherein at least one monomer unit has a backbone comprising aromatic groups and ether linkages. Preferred polyaryl ethers for use in forming compositions and photoconductors in accordance with the present invention include polyaryletherketones (PAEKs), polyarylethersulfones (PAESs), poly(aryl-perfluoroaryl ether)s (PAPFAEs), polyaryletherketones-hydrazones (PAEK-hydrazones), and polyaryletherketone-azines (PAEK-azines) and mixtures and copolymers thereof.
As used herein, xe2x80x9cpolyaryletherketonesxe2x80x9d is intended to refer to polymeric compounds having a polymeric backbone comprising aromatic rings, ether linkages and ketone linkages, while xe2x80x9cpolyarylethersulfonesxe2x80x9d is intended to refer to polymeric compounds having a polymeric backbone comprising aromatic rings, ether linkages and sulfone linkages. xe2x80x9cPolyaryletherketone-azinesxe2x80x9d is intended to refer to PAEK polymers wherein at least one of the ketones of the polymeric backbone has been replaced with an azine, while xe2x80x9cpolyaryletherketones-hydrazonesxe2x80x9d is intended to refer to polymers wherein at least one of the ketones of the polymer backbone has been replaced with a hydrazone. xe2x80x9cPoly(aryl-perfluoroaryl ether)sxe2x80x9d is intended to refer to polymeric compounds having a backbone comprising aromatic groups, at least one of which is perfluorinated, and ether linkages. The polymeric compounds may be homopolymers or copolymers. Preferably the molecular weights of the polymers are from about 2,000 to about 100,000, more preferably from about 10,000 to about 70,000.
There are several ways of synthesizing PAEKs and PAESs, such as a Friedel-Crafts reaction of stoichiometric amounts of aromatic bisbenzoyl chlorides with arenes, a nucleophilic displacement reaction of stoichiometric quantities of bisphenolate salts with activated aromatic dihalides in polar aprotic solvents, and a phase transfer catalyzed nucleophilic displacement reaction of bisphenols with hexafluorobenzene.
The PAEKs and PAESs may be synthesized by the polymerization reaction of stoichiometric amounts of one or more bisphenol compounds, such as bisphenols or bisphenolate salts, with a dihalobenzophenone or a dihalophenylsulfone in a polar aprotic solvent, such as N,N-dimethylacetamide (DMAc), and an azeotroping solvent, such as toluene, under refluxing conditions. In one embodiment, at least two different bisphenol compounds are employed. The reaction is generally catalyzed by a base, preferably an inorganic base such as potassium carbonate (K2CO3), potassium hydroxide (KOH) or cesium fluoride (CsF). Generally two equivalents of the base are used with respect to the bisphenol. The water formed in the reaction may be removed by any convenient means, such as by forming an azeotrope with toluene. The reaction mixture is stirred under refluxing temperature to increase the degree of polymerization. The polymerization may be quenched in water, and the resulting product may be chopped in a high speed blender. The polymer may be isolated by filtration, neutralized, stirred in boiling water, stirred in boiling methanol, and then dried.
While not being bound by theory, the PAEK and PAES reactions are believed to proceed as set forth below in Reaction Sequence 1.
Reaction Sequence 1. Preparation of Polyaryletherketones and Polyarylethersulfones 
Preferred PAEKs and PAESs include those shown in Reaction Sequence 1.
R1 and R3 may be identical or different, and R and R2 may be identical or different. In one embodiment R and R2 are different.
PAEK polymers may be modified to replace at least one of the ketones of the polymeric backbone with an azine or a hydrazone. The modification of a PAEK to the corresponding PAEK-hydrazone may be accomplished by the condensation of the PAEK with a hydrazine, while the modification of a PAEK to the corresponding PAEK-azine may be accomplished by the condensation of the PAEK with a hydrazone. PAEK-hydrazones comprise a group having the general structure: 
while PAEK-azines comprise a group having the general structure: 
The Rxe2x80x2 and Rxe2x80x3 groups may be identical or different, further the Rxe2x80x2 and Rxe2x80x3 groups may be linked to form a ring structure, such as a fluorene structure. As one of ordinary skill will appreciate, the exact structures of the Rxe2x80x2 and Rxe2x80x3 groups depend upon the hydrazines or hydrazones used.
Suitable hydrazines include dialkylhydrazines, diarylhydrazines and aralkylhydrazines, such as 1,1-diphenylhydrazine hydrochloride, phenyl methylhydrazine and dimethylhydrazine, while suitable hydrazones include dialkylhydrazones and aralkylhydrazones, such as 9-fluorenone hydrazone, diarylhydrazone, dialkylhydrazone and aralkyl hydrazone. In one embodiment less than all of the ketone groups of the PAEK are converted, and the resulting polymers are co-polymers of either a ketone and an azine pendant, or a ketone and a hydrazone pendant. While not being bound by theory, the formations of the pendant azines and the pendant hydrazones are believed to proceed as set forth below in Reaction Sequences 2 and 3, respectively.
Reaction Sequence 2. Synthesis of PAEK-azines 
Reaction Sequence 3. Synthesis of PAEK-hydrazones 
Preferred PAEK-azines and PAEK-hydrazones include those set forth in Reaction Sequences 2 and 3, respectively.
PAPFAEs may be synthesized by, for example, the polymerization reaction of stoichiometric amounts of one or more bisphenol compounds, such as bisphenols or bisphenolate salts, with a perfluoro aromatic compound, such as decafluorobiphenyl, perfluorobenzophenone and perfluorophenylsulfone, in N,N-dimethylacetamide. In one embodiment at least two different bisphenol compounds are employed. While not being bound by theory, the reaction is believed to proceed as set forth below in Reaction Sequence 4.
Reaction Sequence 4. Preparation of Poly(aryl-perfluoroaryl Ether )s 
Preferred PAPFAEs include those set forth in Reaction Sequence 4.
The reaction is generally catalyzed by a base, preferably an inorganic base such as potassium carbonate (K2CO3), or cesium fluoride (CsF). Generally two equivalents of the base are used with respect to the bisphenol. The polymerization may be quenched in water, and the resulting product may be chopped in a high speed blender. The polymer may be isolated by filtration, neutralized, stirred in boiling water, stirred in boiling methanol, and then dried.
In the synthesis of the PAPFAEs, the reaction temperature during the polymerization is generally less than the refluxing temperature. As used herein, xe2x80x9crefluxing temperaturexe2x80x9d refers to the temperature at which the solvent boils in the solution. If the reaction temperature is substantially close to the refluxing temperature ( greater than 145xc2x0 C.), the polymerization mixtures become highly viscous and cross-linked. The reaction temperature is a temperature below which such cross-linking occurs. Generally, the reaction temperature is less than 145xc2x0 C., preferably the reaction temperature is from about 50xc2x0 C. to about 140xc2x0 C., more preferably the reaction temperature is about 120xc2x0 C.
Preferred PAPFAEs are soluble in organic solvents. Particularly preferred are PAPFAEs which are soluble in tetrahydrofuran (THF), chlorinated hydrocarbons (such as dichloromethane and chloroform), dioxane and polar aprotic solvents (such as dimethyl acetamide, dimethyl formamide, N-methyl-2-pyrrolidinone and methyl sulfoxide).
The polyaryl ethers may be synthesized using any suitable bisphenol compound. Preferred bisphenol compounds are selected from the group consisting of bisphenol-A, cyclohexylidenebiphenol, fluorenylidenebisphenol, phenolphthalein, methylbisphenol-A, bisphenolate salts and mixtures thereof. In a preferred embodiment the polyaryl ethers are synthesized from two different bisphenol compounds.
Charge Transport Compositions and Layers
Charge transport layers in accordance with the present invention comprise at least one charge transport molecule, polycarbonate and a polyaryl ether selected from the group consisting of polyaryletherketones, poly(arylperfluoro ethers)s, polyaryletherketones-hydrozones, polyaryletherketones-azines and mixtures thereof. The weight ratio of the polycarbonate to the polyaryl ether is generally in the range of from about 93:7 to about 75:25, preferably in the range of from about 93:7 to about 85:15.
Conventional charge transport compounds suitable for use in the charge transport layer of the photoconductors of the present invention should be capable of supporting the injection of photo-generated holes or electrons from the charge generation layer and allowing the transport of these holes or electrons through the charge transport layer to selectively discharge the surface charge. Suitable charge transport compounds for use in the charge transport layer include, but are not limited to, the following:
1. Diamine transport molecules of the types described in U.S. Pat. Nos. 4,306,008, 4,304,829, 4,233,384, 4,115,116, 4,299,897, 4,265,990 and/or 4,081,274. Typical diamine transport molecules include benzidine compounds, including substituted benzidine compounds such as the N,Nxe2x80x2-diphenyl-N,Nxe2x80x2-bis(alkylphenyl)-[1,1xe2x80x2-biphenyl]-4,4xe2x80x2-diamines wherein the alkyl is, for example, methyl, ethyl, propyl, n-butyl, or the like, or halogen substituted derivatives thereof, and the like.
2. Pyrazoline transport molecules as disclosed in U.S. Pat. Nos. 4,315,982, 4,278,746 and 3,837,851. Typical pyrazoline transport molecules include 1-[lepidyl-(2)]-3-(p-diethylaminophenyl)-5-(p-diethylaminophenyl)pyrazoline, 1-[quinolyl-(2)]-3-(p-diethylaminophenyl)-5-(p-diethylaminophenyl)pyrazoline, 1-[pyridyl-(2)]-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline, 1-[6-methoxypyridyl-(2)]-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline, 1-phenyl-3-[p-diethylaminostyryl]-5-(p-dimethylaminostyryl)pyrazoline, 1-phenyl-3-[p-diethylaminostyryl]-5-(p-diethylaminostyryl)pyrazoline, and the like.
3. Substituted fluorene charge transport molecules as described in U.S. Pat. No. 4,245,021. Typical fluorene charge transport molecules include 9-(4xe2x80x2-dimethylaminobenzylidene)fluorene, 9-(4xe2x80x2-methoxybenzylidene)fluorene, 9-(2,4xe2x80x2-dimethoxybenzylidene)fluorene, 2-nitro-9-benzylidene-fluorene, 2-nitro-9-(4xe2x80x2-diethylaminobenzylidene)fluorene and the like.
4. Oxadiazole transport molecules such as 2,5-bis(4-diethylaminophenyl)-1,3,4-oxadiazole, imidazole, triazole, and others as described in German Patents Nos. 1,058,836, 1,060,260 and 1,120,875 and U.S. Pat. No. 3,895,944.
5. Hydrazone transport molecules including p-diethylaminobenzaldehyde-(diphenylhydrazone), p-diphenylaminobenzaldehyde-(diphenylhydrazone), o-ethoxy-p-diethylaminobenzaldehyde-(diphenylhydrazone), o-methyl-p-diethylaminobenzaldehyde-(diphenylhydrazone), o-methyl-p-dimethylaminobenzaldehyde(diphenylhydrazone), p-dipropylaminobenzaldehyde-(diphenylhydrazone), p-diethylaminobenzaldehyde-(benzylphenylhydrazone), p-dibutylaminobenzaldehyde-(diphenylhydrazone), p-dimethylaminobenzaldehyde-(diphenylhydrazone) and the like described, for example, in U.S. Pat. No. 4,150,987. Other hydrazone transport molecules include compounds such as 1-naphthalenecarbaldehyde 1-methyl-1-phenylhydrazone, 1-naphthalenecarbaldehyde 1,1-phenylhydrazone, 4-methoxynaphthlene-1-carbaldehyde 1-methyl-1-phenylhydrazone and other hydrazone transport molecules described, for example, in U.S. Pat. Nos. 4,385,106, 4,338,388, 4,387,147, 4,399,208 and 4,399,207. Yet other hydrazone charge transport molecules include carbazole phenyl hydrazones such as 9-methylcarbazole-3-carbaldehyde-1,1-diphenylhydrazone, 9-ethylcarbazole-3-carbaldehyde-1-methyl-1-phenylhydrazone, 9-ethylcarbazole-3-carbaldehyde-1-ethyl-1-phenylhydrazone, 9-ethylcarbazole-3-carbaldehyde-1-ethyl-1-benzyl-1-phenylhydrazone, 9-ethylcarbazole-3-carbaldehyde-1,1-diphenylhydrazone, and other suitable carbazole phenyl hydrazone transport molecules described, for example, in U.S. Pat. No. 4,256,821. Similar hydrazone transport molecules are described, for example, in U.S. Pat. No. 4,297,426.
Preferably, the charge transport compound included in the charge transport layer comprises a hydrazone, an aromatic amine (including aromatic diamines such as benzidine), a substituted aromatic amine (including substituted aromatic diamines such as substituted benzidines), or a mixture thereof. Preferred hydrazone transport molecules include derivatives of aminobenzaldehydes, cinnamic esters or hydroxylated benzaldehydes. Exemplary aminobenzaldehyde-derived hydrazones include those set forth in the Anderson et al U.S. Pat. Nos. 4,150,987 and 4,362,798, while exemplary cinnamic ester-derived hydrazones and hydroxylated benzaldehyde-derived hydrazones are set forth in the copending Levin et al U.S. Applications Ser. Nos. 08/988,600 and 08/988,791, respectively, all of which patents and applications are incorporated herein by reference.
In one embodiment the charge transport compound comprises a compound selected from the group consisting of poly(N-vinylcarbazole)s, poly(vinylanthracene)s, poly(9,10-anthracenenylene-dodecanedicarboxylate)s, polysilanes, polygermanes, poly(p-phenylene-sulfide), hydrazone compounds, pyrazoline compounds, enamine compounds, styryl compounds, arylmethane compounds, arylamine compounds, butadiene compounds, azine compounds, and mixtures thereof. In a preferred embodiment the charge transport compound comprises a compound selected from the group consisting of p-diethylaminobenzaldehyde-(diphenylhydrazone) (DEH), N,Nxe2x80x2-bis-(3-methylphenyl)-N,Nxe2x80x2-bis-phenyl-benzidine (TPD) and mixtures thereof. TPD has the formula: 
The charge transport layer typically comprises the charge transport compound in an amount of from about 5 to about 60 weight percent, more preferably in an amount of from about 15 to about 40 weight percent, based on the weight of the charge transport layer, with the remainder of the charge transport layer comprising the polycarbonate, the polyaryl ether and any conventional additives.
Suitable polycarbonates include polycarbonate-A""s, polycarbonate-Z""s, and mixtures thereof. Preferred polycarbonates have a number average molecular weight of from about 10,000 to about 100,000, preferably from about 20,000 to about 80,000. A preferred polycarbonate includes a polycarbonate-A having the structure set forth below: 
Such a polycarbonate-A is available from Bayer Corporation as MAKROLON(copyright)-5208 Polycarbonate, having a number average molecular weight of about 34,000.
The polyaryl ethers used in the charge transport layer have a number average molecular weight of at least about 2,000, preferably at least about 5,000, more preferably at least about 10,000, and even more preferably at least about 20,000. The polyaryl ethers generally have a molecular weight no greater than about 100,000, preferably no greater than abut 70,000. In one embodiment, the charge transport layer comprises a polymer selected from the group consisting of polyaryl ether sulfones and polyaryl etherketones having a molecular weight in the range of from about 2,000 to about 100,000, preferably from about 10,000 to about 40,000. In another embodiment, the charge transport layer comprises a polyaryl-perfluoroaryl ether having a number average molecular weight in the range of from about 5,000 to about 100,000, preferably from about 20,000 to about 70,000. In another embodiment, the charge transport layer comprises a polyaryletherketone-hydrazine and/or polyaryletherketone-azine having a number average molecular weight in the range of from about 20,000 to about 100,000, preferably from about 10,000 to about 60,000.
The charge transport layer will typically have a thickness of from about 10 to about 40 microns and may be formed in accordance with conventional techniques known in the art. Conveniently, the charge transport layer may be formed by preparing a charge transport composition, coating the charge transport composition on the respective underlying layer and drying the coating.
To form the charge transport composition according to the present invention, the polycarbonate, polyaryl ether and the charge transport compound are dispersed or dissolved in an organic liquid. Although the composition which forms the charge transport layer may be referred to as a solution, the polycarbonate, polyaryl ether and charge transport compound may disperse rather than dissolve in the organic liquid, thus the composition may be in the form of a dispersion rather than a solution. The polycarbonate, polyaryl ether and charge transport compound may be added to the organic liquid simultaneously or consecutively, in any order of addition. Suitable organic liquids are preferably essentially free of amines and therefore avoid environmental hazards conventionally incurred with the use of amine solvents. Suitable organic liquids include, but are not limited to, tetrahydrofuran, 1,2-dioxane, 1,4-dioxane, and the like. Additional solvents suitable for dispersing the charge transport compound, polycarbonate and polyaryl ether blend will be apparent to those skilled in the art.
The charge transport composition generally comprises, by weight, from about 30% to about 70%, preferably from about 50% to 70%, of the polycarbonate and from about 0.5% to about 30%, preferably from about 0.5% to 15%, of the polyaryl ether. The polycarbonate and the polyaryl ether form a binder blend. The weight ratio of polycarbonate and the polyaryl ether in the binder blend is from about 93:7 to about 75:25, preferably from about 93:7 to about 85:15.
Charge Generation Compositions and Layers
Charge generation layers in accordance with the present invention comprise a charge generation molecule, polyvinylbutyral and a polyaryl ether selected from the group consisting of polyaryletherketones, polyaryl ether sulfones and mixtures thereof. The polyaryletherketones and polyarylether sulfones generally have a number average molecular weight from about 2,000 to about 100,000, preferably from about 10,000 to about 40,000.
Polyvinylbutyral polymers are well known in the art and are commercially available from various sources. These polymers are typically made by condensing polyvinyl alcohol with butyraldehyde in the presence of an acid catalyst, for example sulfuric acid, and contain a repeating unit of formula: 
Typically, the polyvinylbutyral polymer will have a number average molecular weight of from about 20,000 to about 300,000. The weight ratio of the polyvinylbutyral to the polyaryl ether in the charge generation layer is generally in the range of from about 25:75 to about 90:10, preferably from about 25:75 to about 75:25.
Various organic and inorganic charge generation compounds are known in the art, any of which are suitable for use in the charge generation layers of the present invention. One type of charge generation compound which is particularly suitable for use in the charge generation layers of the present invention comprises the squarylium-based pigments, including squaraines. Squarylium pigment may be prepared by an acid route such as that described in U.S. Pat. Nos. 3,617,270, 3,824,099, 4,175,956, 4,486,520 and 4,508,803, which employs simple procedures and apparatus, has a short reaction time and is high in yield. The squarylium pigment is therefore very inexpensive and is easily available.
Preferred squarylium pigments suitable for use in the present invention may be represented by the structural formula: 
wherein R1 represents hydroxy, hydrogen or C1-5 alkyl, preferably hydroxy, hydrogen or methyl, and each R2 individually represents C1-5 alkyl or hydrogen. In a further preferred embodiment, the pigment comprises a hydroxy squaraine pigment wherein each R1 in the formula set forth above comprises hydroxy.
Another type of pigment which is particularly suitable for use in the charge generation layers of the present invention comprises the phthalocyanine-based compounds. Suitable phthalocyanine compounds include both metal-free forms such as the X-form metal-free phthalocyanines and the metal-containing phthalocyanines. In a preferred embodiment, the phthalocyanine charge generation compound may comprise a metal-containing phthalocyanine wherein the metal is a transition metal or a group IIIA metal. Of these metal-containing phthalocyanine charge generation compounds, those containing a transition metal such as copper, titanium or manganese or containing aluminum or gallium as a group IIIA metal are preferred. These metal-containing phthalocyanine charge generation compounds may further include oxy, thiol or dihalo substitution. Titanium-containing phthalocyanines as disclosed in U.S. Pat. Nos. 4,664,997, 4,725,519 and 4,777,251, including oxo-titanyl phthalocyanines, and various polymorphs thereof, for example type IV polymorphs, and derivatives thereof, for example halogen-substituted derivatives such as chlorotitanyl phthalocyanines, are suitable for use in the charge generation layers of the present invention.
Additional conventional charge generation compounds known in the art, including, but not limited to, disazo compounds, for example as disclosed in the Ishikawa et al U.S. Pat. No. 4,413,045, and tris and tetrakis compounds as known in the art, are also suitable for use in the charge generation layers of the present invention. It is also within the scope of this invention to employ a mixture of charge generation pigments or compounds in the charge generation layer.
In one embodiment of the invention, the charge generation molecule is a pigment selected from the group consisting of azo pigments, anthraquinone pigments, polycyclic quinone pigments, indigo pigments, diphenylmethane pigments, azine pigments, cyanine pigments, quinoline pigments, benzoquinone pigments, napthoquinone pigments, naphthalkoxide pigments, perylene pigments, fluorenone pigments, squarylium pigments, azuleinum pigments, quinacridone pigments, phthalocyanine pigments, naphthaloxyanine pigments, porphyrin pigments and mixtures thereof. In a preferred embodiment, the charge generation molecule is a pigment selected from the group consisting of hydroxy squaraines, Type IV oxotitanium phthalocyanines, and mixtures thereof.
The charge generation layers may comprise the charge generation compound in amounts conventionally used in the art. Typically, the charge generation layer may comprise from about 5 to about 80, preferably at least about 10, and more preferably from about 15 to about 60, weight percent of the charge generation compound, and may comprise from about 20 to about 95, preferably not more than about 90, and more preferably comprises from about 40 to about 85, weight percent of the total of the polyvinylbutryal and the polyaryl ether, all weight percentages being based on the charge generation layer. The charge generation layers may further contain any conventional additives known in the art for use in charge generation layers.
To form the charge generation layers according to the present invention, the polyvinylbutryal, polyaryl ether and the charge generation compound are dissolved and dispersed, respectively, in an organic liquid. Although the organic liquid may generally be referred to as a solvent, and typically dissolves the polyvinylbutryal and the polyaryl ether, the liquid technically forms a dispersion of the pigment rather than a solution. The polyvinylbutryal, polyaryl ether and pigment may be added to the organic liquid simultaneously or consecutively, in any order of addition. Suitable organic liquids are preferably essentially free of amines and therefore avoid environmental hazards conventionally incurred with the use of amine solvents. Suitable organic liquids include, but are not limited to, tetrahydrofuran, cyclopentanone, 2-butanone and the like. Additional solvents suitable for dispersing the charge generation compound, polyvinylbutryal and polyaryl ether blend will be apparent to those skilled in the art.
The charge generation composition generally comprises, by weight, from about 0.5% to 20%, preferably from about 1% to 7%, of the polyvinylbutyral and from about from about 0.5% to 20%, preferably from about 0.5% to 3%, of the polyaryl ether. The polyvinylbutyral and the polyaryl ether form a binder blend. In one embodiment the binder blend comprises, by weight, 0.5% to 3% polyvinylbutyral and 0.5% to 3% polyaryl ether. The weight ratio of polyvinylbutyral and the polyaryl ether in the binder blend is from about 95:5 to about 5:95, preferably from about 75:25 to about 25:75.
In accordance with techniques generally known in the art, the composition preferably contains not greater than about 10 weight percent solids comprising the polyvinylbutryal, the polyaryl ether and charge generation compound in combination. The compositions may therefore be used to form a charge generation layer of desired thickness, typically not greater than about 5 microns, and more preferably not greater than about 1 micron, in thickness. Additionally, a homogeneous layer may be easily formed using conventional techniques, for example dip coating or the like. These compositions also reduce any wash or leach of the charge generation compound into a charge transport layer coating which is subsequently applied to the charge generation layer.
The charge generation layers according to the present invention exhibit good adhesion to underlying layers. Typically, the charge generation layer will be applied to a photoconductor substrate, with a charge transport layer formed on the charge generation layer. In accordance with techniques known in the art, one or more barrier layers may be provided between the substrate and the charge generation layer. Typically, such barrier layers have a thickness of from about 0.05 to about 20 microns. It is equally within the scope of the present invention that the charge transport layer is first formed on the photoconductor substrate, followed by formation of the charge generation layer on the charge transport layer.
Photoconductors
The photoconductor substrate may be flexible, for example in the form of a flexible web or a belt, or inflexible, for example in the form of a drum. Typically, the photoconductor substrate is uniformly coated with a thin layer of a metal, preferably aluminum, which functions as an electrical ground plane. In a further preferred embodiment, the aluminum is anodized to convert the aluminum surface into a thicker aluminum oxide surface. Alternatively, the ground plane member may comprise a metallic plate formed, for example, from aluminum or nickel, a metallic drum or foil, or a plastic film on which aluminum, tin oxide, indium oxide or the like is vacuum evaporated. Typically, the photoconductor substrate will have a thickness adequate to provide the required mechanical stability. For example, flexible web substrates generally have a thickness of from about 0.01 to about 0.1 microns, while drum substrates generally have a thickness of from about 0.75 mm to about 1 mm.